1. Field of the Invention
The present invention relates to a composite thin-film magnetic head comprising a read head and a write head and a method of manufacturing such a thin-film magnetic head.
2. Description of the Related Art
Performance improvements in thin-film magnetic heads have been sought as the recording density of hard disk drives has increased. Consequently, in place of thin-film magnetic heads incorporating an induction-type electromagnetic transducer that performs reading and writing, composite thin-film magnetic heads have been widely used. A composite head is made up of a combination of a write (recording) head having an induction-type electromagnetic transducer for writing and a read (reproducing) head having a magnetoresistive (MR) element for reading.
Reference is now made to FIG. 11 and FIG. 12 to describe examples of the configuration of related-art composite thin-film magnetic heads. FIG. 11 is a cross section of one of the examples of the configuration of the thin-film magnetic heads wherein a single layer functions as both one of shield layers of a read head and a magnetic pole layer of a write head that forms one of the magnetic poles. FIG. 12 is a cross section of the other of the examples of the configuration of the thin-film magnetic heads wherein a write head and a read head are separated.
The thin-film magnetic head of FIG. 11 comprises: a substrate 101 made of a ceramic material such as aluminum oxide and titanium carbide (Al2O3—TiC); an insulating layer 102 made of an insulting material such as alumina (Al2O3) and formed on the substrate 101; a read (reproducing) head formed on the insulating layer 102; a write (recording) head formed on the read head; and an overcoat layer 118 covering the write head.
The read head comprises: a bottom shield layer 103 made of a magnetic material and formed on the insulating layer 102; a bottom shield gap film 104 made of an insulating material such as alumina and formed on the bottom shield layer 103; and an MR element 105 for reading formed on the bottom shield gap film 104 and having an end located in the air bearing surface (the medium facing surface that faces toward a recording medium). The read head further comprises: a pair of lead layers 106 formed on the bottom shield gap film 104 and electrically connected to the MR element 105; a top shield gap film 107 covering the bottom shield gap film 104, the MR element 105 and the lead layers 106; and a top-shield-layer-cum-bottom-pole-layer (hereinafter called a bottom pole layer) 110 made of a magnetic material and formed on the top shield gap film 107.
The write head comprises: the bottom pole layer 110; a write gap layer 111 made of an insulating material such as alumina and formed on the bottom pole layer 110; and a top pole layer 117 made of a magnetic material and formed on the write gap layer 111. The overcoat layer 118 is made of an insulating material such as alumina and covers the top pole layer 117.
Each of the bottom pole layer 110 and the top pole layer 117 has a magnetic pole portion that is a portion located on a side of the air bearing surface. These pole portions are opposed to each other, the gap layer 111 being located between the pole portions. Although not shown, the top pole layer 117 has an end located farther from the air bearing surface. This end of the top pole layer 117 is connected and magnetically coupled to the bottom pole layer 110 through a contact hole formed in the write gap layer 111. Although not shown, a thin-film coil is provided between the bottom pole layer 110 and the top pole layer 117, the coil being insulated therefrom.
The thin-film magnetic head of FIG. 12 comprises: the substrate 101 made of a ceramic material such as aluminum oxide and titanium carbide; the insulating layer 102 made of an insulting material such as alumina and formed on the substrate 101; the read head formed on the insulating layer 102; the write head formed on the read head; the overcoat layer 118 covering the write head; and a magnetism intercepting layer 109, provided between the read head and the write head, for intercepting magnetism.
As the thin-film magnetic head of FIG. 11, the read head comprises: the bottom shield layer 103, the bottom shield gap film 104, the MR element 105, the lead layers 106, and the top shield gap film 107. In addition, the read head comprises a top shield layer 108 made of a magnetic material and formed on the top shield gap film 107.
The write head comprises: the bottom pole layer 110; the write gap layer 111 made of an insulating material such as alumina and formed on the bottom pole layer 110; and the top pole layer 117 made of a magnetic material and formed on the write gap layer 111.
In the thin-film magnetic head of FIG. 12, the magnetism intercepting layer 109 is provided between the top shield layer 108 and the bottom pole layer 110.
The configuration of thin-film magnetic heads that was initially common is the one in which the write head and the read head are separated, as shown in FIG. 12. The configuration of thin-film magnetic heads that was proposed thereafter is the one in which the top shield layer of the read head and the bottom pole layer of the write head are merged, as shown in FIG. 11, in response to the demands for, for example, streamlining the manufacturing process and for minimizing the space between the write gap layer and the MR element. Many heads have been thus designed to have such a configuration. (See David Hannon et al., ‘Allicat Magnetoresistive Head Design and Performance’, IEEE Transaction on Magnetics, Vol. 30, No. 2, pp. 298 to 302, March 1994.)
However, if the read track width of the thin-film magnetic head is reduced and improvements in the performance of the read head, such as an increase in sensitivity of the MR element, are thereby promoted, pulse-shaped noise may be produced in a read signal when reading is performed immediately after writing, the noise having a peak value extremely higher than that of normal white noise. This noise is considered to result from relaxation of magnetization in the top shield layer caused by the magnetic field applied to the top shield layer while writing is performed by the write head. Alternatively, the noise is considered to result from relaxation of magnetization of the MR element that occurs when a strong magnetic field created by the top shield layer is directly applied to the MR element. Such noise resulting from unstable magnetization immediately after writing is called write induced noise in the present patent application. The frequency of occurrence of this noise increases as the sensitivity of the MR element increases. The occurrences of servo errors and so on thereby increase and become a great factor that reduces the response rate of the hard disk drive.
Since such problems have frequently arisen, the configuration of thin-film magnetic heads in which the write head and the read head are separated, as shown in FIG. 12, have been adopted again.
However, the space between the write gap layer and the MR element is greater in the head having the write head and the read head separated. In the head shown in FIG. 12, for example, the space between the write gap layer 111 and the MR element 105 is greater than 5.5 μm, if the top shield layer 108 is 2.5 μm thick, the magnetism intercepting layer 109 is 0.5 to 1 μm thick, and the bottom pole layer 110 is 2.5 μm thick. In the high-density composite thin-film magnetic head, it is disadvantageous that the space between the write gap layer and the MR element is increased when servo control is performed.
In addition, it is required to fabricate the top shield layer, the magnetism intercepting layer and the bottom pole layer separately for the related-art head in which the write head and the read head are separated by the magnetism intercepting layer. As a result, not only the period of time required for manufacturing increases but also an increase in the number of manufacturing steps leads to an increase in costs.
Reference is now made to FIG. 13 to FIG. 25 to describe this problem. FIG. 13 to FIG. 25 are cross sections for illustrating an example of method of forming the top shield layer, the magnetism intercepting layer and the bottom pole layer. In this method, as shown in FIG. 13, a bonding layer 152 made of titanium (Ti), for example, is formed, as required, on a layer 151 to be the base of the top shield layer. The bonding layer 152 is provided for increasing the adhesiveness of the layer 151 to an electrode film described later. Next, on the bonding layer 152, the electrode film 153 is formed for making the top shield layer through plating.
Next, as shown in FIG. 14, a resist is patterned into a specific shape to form a frame 154 used for making the top shield layer.
Next, as shown in FIG. 15, frame plating is performed, using the frame 154, to form plating layers 155A and 155B on the electrode film 153. Numeral 155A indicates the plating layer to be the top shield layer. Numeral 155B indicates the other plating layers. Next, as shown in FIG. 16, the frame 154 is removed.
Next, as shown in FIG. 17, a portion of the electrode film 153 located in the region where the frame 154 was located is removed through ion milling, for example.
Next, as shown in FIG. 18, a patterned resist 156 is formed to cover the plating layer 155A.
Next, as shown in FIG. 19, the plating layers 155B that are not covered with the patterned resist 156 are removed. Next, as shown in FIG. 20, the patterned resist 156 is removed.
Next, as shown in FIG. 21, the bonding layer 152 except a portion thereof located below the plating layer 155A is removed through ion milling, for example.
Next, as shown in FIG. 22, the magnetism intercepting layer 157 made of inorganic oxide is formed over the entire surface through sputtering, for example.
Next, although not shown, a portion of the magnetism intercepting layer 157 in which the electrode layer is to be formed is etched, so that conduction is made between the lead layers connected to the MR element and the electrode layer to be formed on the magnetism intercepting layer 157. For this etching, on the magnetism intercepting layer 157, a patterned resist is formed to cover the layer 157 except the portion thereof in which the electrode layer is to be formed. Next, using this patterned resist as a mask, the portion of the layer 157 in which the electrode layer is to be formed is etched through ion milling, for example. The patterned resist is then removed.
Next, as shown in FIG. 23, a bonding layer 158 made of titanium (Ti), for example, is formed, as required, on the magnetism intercepting layer 157. Next, on the bonding layer 158, the electrode film 159 is formed for making the bottom pole layer through plating.
Next, as shown in FIG. 24, a resist is patterned into a specific shape to form a frame 160 used for making the bottom pole layer.
Next, as shown in FIG. 25, plating is performed, using the frame 160, to form plating layers 161A and 161B. Numeral 161A indicates the plating layer to be the bottom pole layer. Numeral 161B indicates the other plating layers.
As thus described, a great number of steps are required to fabricate the top shield layer, the magnetism intercepting layer and the bottom pole layer of the related-art head in which the write head and the read head are separated by the magnetism intercepting layer.